Ink

Abstract: Disclosed herein is an ink comprising a coloring material and a liquid medium dissolving the coloring material therein, wherein the ink comprises a dye having at least one ammonium ion as a counter ion and an ammonium salt of an inorganic or organic acid.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an ink. In particular, it relates to an ink which can provide images excellent in water fastness on non-coated paper such as paper for copying, paper for reporting, notepaper, letter paper, bond paper and continuous business forms, i.e., so-called plain paper, which are commonly used in offices and homes, and is excellent in solution stability and suitable for use in a system capable of high-image quality recording using bubble-jet printer. The present invention also relates to an ink-jet recording ink, and particularly to an ink which can provide images excellent in water fastness on all recording materials, in particular, non-coated paper such as paper for copying, paper for reporting, notepaper, letter paper, bond paper and continuous business forms, i.e., so-called plain paper, which are commonly used in offices and homes, has an ideal black color, and is excellent in solution stability and suitable for use in a system capable of high-image quality recording using bubble-jet printer. Further, this invention relates to an ink capable of conducting recording free of feathering and unevenness of color strength on plain paper. Related Background Art Inks with greatly various manners of being composed have been hitherto reported in respect of inks for ink-jet recording. In particular, in recent years, detailed researches and developments have been made from various aspects such as compositions and physical properties of inks because of a demand for improving the water fastness of images upon recording on plain paper such as paper for copying, paper for reporting, notepaper, letter paper, bond paper and continuous business forms, which are commonly used in offices. For example, Japanese Patent Application Laid-Open Nos. 2-296878 and 2-255876 have proposed to contain a polyamine in a water-based ink composition. In such an ink, however, the polyamine forms a salt with a hydrophilic group in a dye contained in the ink, and so the solution stability of the ink is lowered. Therefore, there are potential problems of reduction in reliability such as clogging at the tip of an orifice, and of bronzing (association of the dye) on a recording material, which may result in unevenness of printing and/or low density. It has also been considered to contain a dissolution stabilizer in the ink for a purpose of improving the solution stability of the ink. In this case, however, it is necessary to contain a great amount of the dissolution stabilizer in the ink, so that the image quality of prints formed with such an ink becomes deteriorated. Besides, Japanese Patent Application Laid-Open No. 3-91577 has proposed to improve the water fastness of images by providing a dye having at least one carboxyl group in which the carboxyl group is formed into an ammonium salt or a volatile substituted ammonium salt, whereby ammonia or amine vaporizes on a recorded article to form a free acid. Even in this case, however, ammonia or amine gradually vaporizes in the ink, and so the solubility of the dye is lowered, which may often form the cause of clogging at an orifice and reduction in stability of the ink though the initial solubility of the ink is good. For the same reason, bronzing tends to occur on a recording material, in particular, on acid paper. The color tone of the dye described in Japanese Patent Application Laid-Open No. 3-91577 is somewhat royal-purplish, and a problem of the color tone hence remains unsolved. Such a problem of color tone have had importance with the advance of color recording. More specifically, when black-color printing is conducted, it is of course ideal for a black ink to have a black color near a primary color as much as possible. Further, full-color printing requires for attaining ideal color reproduction well-balanced that in addition to magenta, yellow and cyan inks, a black ink should produce a color near a primary color. Besides, EP 0468647 Al, EP 0468648 Al and EP 0468649 Al describe disazo dyes and phthalocyanine dyes having at least one carboxyl group. Further, U.S. Patent No. 4,963,189 describes disazo dyes having at least one carboxyl group. However, these dyes are originally hard to be dissolved in water, so that the water fastness of prints formed from an ink containing such a dye is improved compared with the conventionally-used inks. However, these dyes tend to cause a disadvantage that when such a dye is dissolved in water or a solvent to prepare an ink, the water or solvent evaporates where a cartridge containing the ink is left over for a long period of time, for example, so that the ink becomes highly viscous, dried and lastly solidified, resulting in failure of printing (such a condition will hereinafter be called "crusting"). Similarly, they may cause a disadvantage that stable ejection of the ink cannot be conducted during printing, or in the case where after the ink is ejected from an orifice, the ejection of the ink is suspended for a certain period of time (for example, 1 minute) and a first droplet of the ink is then ejected from that orifice, resulting in uneven printing (such a condition will hereinafter be called "poor first-ejection"). U.S. Patent Nos. 4,963,189, 5,062893 and 5,062,892 disclose techniques of reducing kogation, i.e. a phenomenon that some components of ink are thermally decomposed and built up on a heater element of an ink-jet head and of adding 0.2 % by weight (0.02 mol/ℓ, 0.58 mol/mol of dye) of sodium phosphate as a pH buffer to an ink. They also disclose a technique of adding an oxo anion to reduce the kogation on the heater. The above techniques cannot provide images free of unevenness of color strength and satisfactory in print density. With respect to recording apparatus, those of very various systems have heretofore been reported. For example, Japanese Patent Application Laid-Open No. 58-36465 discloses an ink On-Demand printing system making use of ink-containing capillary tubes having orifices through which an ink is ejected. In such an ink On-Demand printing system, an ink-heating element is arranged in close vicinity to each of the orifices. For this reason, each ink-containing capillary tube or a heating resistor provided in the vicinity thereof is rapidly heated, and moreover transfers a large amount of thermal energy to the ink in close vicinity to the orifice, whereby a minute part of the ink is vaporized to generate bubbles in the capillary tube. In consequence, the bubbles generate a pressure wave by which an ink droplet is ejected out of the orifice on the surface of a recording material. If the position of the ink-heating element to the orifice is suitably preset, and the transfer of energy from the heating element to the ink is carefully controlled, the bubbles vanish on the ink-heating element or in the vicinity thereof before the vapor escapes from the orifice. The service life of such a thermal ink-jet printer is known to depend on, in particular, the service lives of an electric conductor and a heating resistor. Remarkable troubles arising on such electric conductor and heating resistor are caused by cavitation damage due to vanishing of bubbles and chemical damage by ink. Therefore, in order to elongate the service life of the thermal ink-jet printer, it is desirable to prevent the fatigue of the heating resistor due to chemical change and check the damage due to the occurrence of cavitation to the minimum. In this regard, for example, Japanese patent Application Laid-Open No. 59-109372 discloses a solution for reducing the fatigue of a heating resistor. More specifically, a heating resistor is generally covered with an inert layer for protecting it against chemical fatigue and mechanical fatigue during its operation. In this publication, a thin layer of silicon carbide, silicon oxide or aluminum oxide is disclosed as the inert layer. Japanese patent Application Laid-Open No. 59-95157 also discloses the use of silicon-oxynitride, aluminum oxide or titanium oxide in addition to silicon dioxide as an inert layer or a protective layer, in which a layer is first formed on a orifice plate, and a heating resistor and an electric conductor are covered with these inert layers. Further, Japanese Patent Application Laid-Open No. 58-221341 discloses that a similar inert layer formed of silicon dioxide or silicon carbide is coated on a heating resistor (tantalum/aluminum alloy) and a electric conductor (aluminum), both, formed in advance. Moreover, Japanese patent Application Laid-Open No. 59-100214 discloses a structure of an inert layer composed of two layers of silicon carbide and silicon nitride or silicon oxide. In each of the publications, the surface protection of the heating resistor and the like making use of the inert substances as described above has been fully satisfactory as to the fatigue properties. However, if cracks and/or pinholes exist in the inert layer or surface-protective layer composed of the inert substance and provided on the heating resistor, the surface-protective layer has involved a problem that it cannot exhibit the desired properties. In particular, if the surface-protective layer is in contact with a liquid (for example, an ink), the ink comes into contact with the heating resistor through these cracks and/or pinholes, so that a metal making up the heating resistor is corroded by the ink, resulting in electrical disconnection of the resistor. As a result, heat is not transferred to the ink, and so a uniform size of ink droplets cannot be ejected out of an ink-jet head at an even rate and in a fixed orbit. On the other hand, it is difficult to completely do away with the cracks and pinholes in the surface-protective layer in a practical production process of the heating resistors. There is hence a demand for early solving the above problem. Furthermore, U.S. Patent No. 5,062,892 also discloses inks for thermal ink-jet, which contain an oxo anion such as a phosphate, a sulfate or an oxalate. Such inks involve a problem that they dissolve surface-protective layers provided on an electric conductor and a heating resistor and cause chemical damage due to kogation, resulting in failure in ejection of ink. EP-A-0 359 376 discloses a recording liquid comprising dyes and a liquid medium, wherein the dyes comprises a black dye and a toning water-soluble dye in combination. Further, the black dye is selected from C.I. Food Black 1, C.I. Acid Black 140 and C.I. Acid Black 187. SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide a black ink and a color ink which can prevent bronzing on a recording material without adversely affecting the water fastness and quality of images when recorded on non-coated paper such as paper for copying, paper for reporting, notepaper, letter paper, bond paper and continuous business forms, i.e., so-called plain paper, which are commonly used in offices and homes, and can solve problems of clogging and storage stability. Another object of the present invention is to provide an ink which provides prints good in water fastness using various kinds of plain paper, causes no clogging in an orifice without adversely affecting the quality of images even after stored for a long period of time and can ensure reliability such as storage stability of the ink. A further object of the present invention is to provide an ink excellent in reliability, in which ink droplets are stably formed even when the ejection of the ink is suspended and then resumed, and no irregularity of print occurs. A still further object of the present invention is to provide an ink which can provide images excellent in water fastness when recorded on plain paper, has an ideal black color and is excellent in solution stability. A yet still further object of the present invention is to provide an ink which can provide high-quality images high in density and free of undefined or irregular feathering and can solve problems of clogging at nozzles and storage stability. The above objects can be achieved by the present invention described below. In the present invention, there is provided an ink comprising a coloring material and a liquid medium dissolving the coloring material therein, wherein the coloring material comprises at least one of dyes represented by the structural formula wherein R is NH 4 and Y is H or SO 3 R, and at least one yellow dye selected from C.I. Acid Yellow 17:1, C.I. Acid Yellow 23, C.I. Acid Yellow 49, C.I. Acid Yellow 65, C.I. Acid Yellow 104, C.I. Acid Yellow 183, C.I. Acid yellow 155, C.I. Acid Yellow 194, C.I. Direct Yellow 86, C.I. Direct Yellow 106, C.I. Direct Yellow 142 and C.I. Direct Yellow 194, and the liquid medium comprises at least one polyhydric alcohol and an aliphatic monohydric alcohol and contains urea, an ammonium salt of an inorganic acid and a hydroxide. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic longitudinal cross-sectional view of a head used in an ink-jet recording system according to the present invention. Fig. 2 is a schematic transverse cross-sectional view of the head taken along line A-B of Fig. 1. Fig. 3 is a schematic illustration showing the appearance of an illustrative multi-head which is an array of such heads as shown in Fig. 1. Fig. 4 is a schematic perspective view showing an illustrative ink-jet recording apparatus in which the head has been incorporated. Fig. 5 is a schematic longitudinal cross-sectional view showing an ink cartridge from which an ink is fed to the head. Fig. 6 is a schematic illustration showing principal parts of an ink-jet recording apparatus in which the head and the ink cartridge have been integrated with each other. Fig. 7 is a schematic illustration of a withstand voltage meter used in the embodiments of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have carried out an extensive investigation on various manners of ink compositions with a view toward improving the solution stability of inks which provide prints excellent in water fastness, and preventing bronzing on a recording material. The present inventors have carried out an extensive investigation on various manners of ink compositions with a view toward obtaining an ink which provides prints excellent in water fastness, is good in solution stability and has a black color near a primary color. As a result, it has been found that when a specific yellow dye is used as a coloring material in combination with a dye represented by the structural formula (a), and a specific medium is used, an ideal black ink which provides high-quality images higher in density and free from undefined or irregular feathering without impairing the water fastness inherent in the dye of the structural formula (a), causes no clogging at nozzles and has good storage stability is obtained, thus leading to completion of the present invention. The yellow dye includes at least one selected from the group consisting of C.I. Acid Yellow 17:1, C.I. Acid Yellow 23, C.I. Acid Yellow 49, C.I. Acid Yellow 65, C.I. Acid Yellow 104, C.I. Acid Yellow 183, C.I. Acid yellow 155, C.I. Acid Yellow 194, C.I. Direct Yellow 86, C.I. Direct Yellow 106, C.I. Direct Yellow 142 and C.I. Direct Yellow 194. The present invention will then be described in detail with reference to preferred embodiments. The total content of the dye represented by the structural formula (a) and the above-described yellow dye, which are used as coloring materials in the present invention, in the ink is preferably within a range of from 0.1 to 15 % by weight, more preferably from 0.1 to 10 % by weight. A mixing ratio of the dye represented by the structural formula (a) to the yellow dye is preferably within a range of from 40:1 to 4:1, more preferably from 20:1 to 5:1 by weight. More specifically, if the mixing ratio of the yellow dye is lower than the lower limit, the color tone is bluish. If the mixing ratio of the yellow dye is higher than the upper limit on the contrary, the color tone is greenish. It is hence impossible to produce an ideal black color at any ratios outside the above range. The combined use of the dye represented by the structural formula (a) and the yellow dye, i.e., the use of plural kinds of dyes, makes the dissolution stability of the dyes enhanced compared with the single use of a dye, resulting in an ink hard to cause clogging at nozzles. Preferable examples of the polyhydric alcohol used in the present invention include ethylene glycol, diethylene glycol, thiodiglycol and glycerol. Besides the polyhydric alcohols, glycol ethers, glycol ether esters, amides, nitrogen-containing heterocyclic ketones and the like are generally known as liquid media. However, at least one polyhydric alcohol is used in the present invention taking into consideration the fact that polyhydric alcohols are good in dissolvability for dyes, and hence cause no clogging, that they are hard to cause feathering on prints, but comparatively good in fixing ability, and moreover that there is no fear of safety such as offensive odor and toxicity compared with nitrogen-containing compounds which are generally high in dissolving power for dyes. The ink according to the present invention further comprises urea. The contents of the polyhydric alcohol and urea in the ink are each preferably within a range of from 1 to 15 % by weight from the viewpoint of clogging, feathering and fixing ability. The aliphatic monohydric alcohol used in the present invention is essential for controlling the fixing ability of the ink on a recording material, i.e., drying ability, and has an effect of facilitating the fixing without causing undefined or irregular feathering. Examples of the aliphatic monohydric alcohol include methanol, ethyl alcohol, isopropyl alcohol, 2-butanol and the like. Its content in the ink is preferably within a range of from 0.1 to 5 % by weight. The ink according to the present invention further comprises the hydroxide and the ammonium salt of an inorganic acid. The single use of the hydroxide can enhance the solubility of the dyes, but deteriorates the water fastness of the dyes. Besides, the single use of the ammonium salt of the inorganic acid can also enhance the solubility of the dyes, but its effect is lower than that of the hydroxide. However, the combined use of the hydroxide and the ammonium salt of the inorganic acid results in an ink having the following effects. Namely, the solution stability of the ink is improved to an extent greater than that of the ink containing only the ammonium salt of the inorganic acid without impairing good water fastness inherent in the dyes, clogging at nozzles is hard to occur, the occurrence of bronzing on recording materials can be suppressed, and stable ejection can be achieved. Examples of the ammonium salt of the inorganic acid include ammonium carbonate, ammonium chloride, ammonium phosphate, ammonium borate, ammonium acetate, ammonium sulfate and the like. Of these, ammonium sulfate is particularly preferred. Examples of the hydroxide include lithium hydroxide, sodium hydroxide, ammonium hydroxide and the like. Of these, sodium hydroxide and lithium hydroxide are particularly preferred. It is preferable to control the contents of these components in the ink each within a range of from 0.1 to 1.0 % by weight and keep the pH of the ink 7 to 10. The inks according to the present invention may suitably be used, in particular, in an ink-jet recording system of a type that recording is conducted by ejecting droplets of an ink by the action of thermal energy. However, the inks may also be used for general-purpose writing utensils. As preferred methods and apparatus for conducting recording by using the inks according to the present invention, may be mentioned a method and apparatus in which thermal energy corresponding to recording signals is applied to an ink within a recording head, and ink droplets are generated in accordance with the thermal energy. Examples of the construction of an head, which is a main component of such an apparatus, are illustrated in Figs. 1, 2 and 3. A head 13 is formed by bonding a glass, ceramic or plastic plate or the like having a groove through which an ink is passed, to a heating head 15, which is used for thermal recording (the drawing shows a head to which, however, is not limited). The heating head 15 is composed of a protective film 16 made of silicon oxide or the like, aluminum electrodes 17-1 and 17-2, a heating resistor layer 18 made of nichrome or the like, a heat accumulating layer 19, and a substrate 20 made of alumina or the like having a good heat radiating property. An ink 21 comes up to an ejection orifice 22 (a minute opening) and forms a meniscus 23 owing to a pressure P. Now, upon application of electric signal information to the electrodes 17-1, 17-2, the heating head 15 rapidly generates heat at the region of thermal action surface 109 to form bubbles in the ink 21 which is in contact with this region. The meniscus 23 of the ink is projected by the action of the pressure thus produced, and the ink 21 is ejected from the orifice 22 to a recording material 25 in the form of recording droplets 24. Fig. 3 illustrates an appearance of a multi-head composed of an array of a number of heads as shown in Fig. 1. The multi-head is formed by closely bonding a glass plate 27 having a number of channels 26 to a heating head 28 similar to the head as illustrated in Fig. 1. Incidentally, Fig. 1 is a cross-sectional view of the head 13 taken along the flow path of the ink, and Fig. 2 is a cross-sectional view taken along line A-B of Fig. 1. Fig. 4 illustrates an example of an ink-jet recording apparatus in which such a head has been incorporated. In Fig. 4, reference numeral 61 designates a blade serving as a wiping member, one end of which is a stationary end held by a blade-holding member to form a cantilever. The blade 61 is provided at a position adjacent to a region in which a recording head operates, and in this embodiment, is held in such a form that it protrudes to the course through which the recording head is moved. Reference numeral 62 indicates a cap, which is provided at a home position adjacent to the blade 61, and is so constituted that it moves in a direction perpendicular to a direction in which the recording head is moved and comes into contact with the face of ejection openings to cap it. Reference numeral 63 denotes an ink-absorbing member provided adjoiningly to the blade 61 and, similar to the blade 61, held in such a form that it protrudes to the course through which the recording head is moved. The above-described blade 61, cap 62 and absorbing member 63 constitute a recovery portion 64 for the recording head, where the blade 61 and the absorbing member 63 remove off water, dust and/or the like from the face of the ink-ejecting openings. If an ink obtained by adding a phosphate singly or in combination with other additives as described in U.S. Patent No. 5,062,892 is used, an Sn ion contained in the absorbing member 63 is dissolved out by a phosphate ion, so that chemical deposit due to kogation is formed on a thermal action surface 109. This offers a problem that the service life of the electrothermal convertor is lowered to a significant extent. Reference numeral 65 designates the recording head having an ejection-energy-generating means and serving to eject the ink onto a recording material set in an opposing relation with the ejection opening face provided with ejection openings to conduct recording. Reference numeral 66 indicates a carriage on which the recording head 65 is mounted so that the recording head 65 can be moved. The carriage 66 is slidably interlocked with a guide rod 67 and is connected (not illustrated) at its part to a belt 69 driven by a motor 68. Thus, the carriage 66 can be moved along the guide rod 67 and hence, the recording head 65 can be moved from a recording region to a region adjacent thereto. Reference numerals 51 and 52 denote a paper feeding part from which the recording materials are separately inserted, and paper feed rollers driven by a motor (not illustrated), respectively. With such construction, the recording material is fed to the position opposite to the ejection opening face of the recording head, and discharged from a paper discharge section provided with paper discharge rollers 53 with the progress of recording. In the above constitution, the cap 62 in the head recovery portion 64 is receded from the moving course of the recording head 65 when the recording head 65 is returned to its home position, for example, after completion of recording, and the blade 61 remains protruded to the moving course. As a result, the ejection opening face of the recording head 65 is wiped. When the cap 62 comes into contact with the ejection opening face of the recording head 65 to cap it, the cap 62 is moved so as to protrude to the moving course of the recording head. When the recording head 65 is moved from its home position to the position at which recording is started, the cap 62 and the blade 61 are at the same positions as the positions upon the wiping as described above. As a result, the ejection opening face of the recording head 65 is also wiped at the time of this movement. The above movement of the recording head to its home position is made not only when the recording is completed or the recording head is recovered for ejection, but also when the recording head is moved between recording regions for the purpose of recording, during which it is moved' to the home position adjacent to each recording region at given intervals, where the ejection opening face is wiped in accordance with this movement. Fig. 5 illustrates an exemplary ink cartridge in which an ink fed to the head through an ink-feeding member, for example, a tube is contained. Here, reference numeral 40 designates an ink container portion containing the ink to be fed, as exemplified by a bag for the ink. One end thereof is provided with a stopper 42 made of rubber. A needle (not illustrated) may be inserted into this stopper 42 so that the ink in the bag 40 for the ink can be fed to the head. Reference numeral 44 indicates an ink-absorbing member for receiving a waste ink. It is preferred for this invention that the ink container portion is formed of a polyolefin, in particular, polyethylene, at its surface with which the ink comes into contact. The ink-jet recording apparatus used for this invention may not be limited to the apparatus as described above in which the head and the ink cartridge are separately provided. Therefore, a device in which these members are integrally formed as shown in Fig. 6 can also be preferably used. In Fig. 6, reference numeral 70 designates a recording unit, in the interior of which an ink container portion containing an ink, for example, an ink-absorbing member, is contained. The recording unit 70 is so constructed that the ink in such an ink-absorbing member is ejected in the form of ink droplets through a head 71 having a plurality of orifices. For this invention, polyurethane, cellulose or polyvinyl acetal is preferably used as a material for the ink-absorbing member. Reference numeral 72 indicates an air passage for communicating the interior of the recording unit 70 with the atmosphere. This recording unit 70 can be used in place of the recording head shown in Fig. 3, and is detachably installed on the carriage 66. The present invention will hereinafter be described more specifically by the following Examples and Comparative Examples. Incidentally, all designations of "part" or "parts" and "%" as will be used in the following examples mean part or parts by weight and % by weight unless expressly noted. Examples 1 to 6: After their corresponding components as shown in Table 1 were mixed and thoroughly stirred into solutions, the resulting solutions were separately filtered under pressure through a "Fluoropore Filter" (trade name; product of Sumitomo Electric Industries, Ltd.) having a pore size of 0.45 µm, thereby preparing respective inks according to Examples 1 to 6 of the present invention. Referential Examples 1 to 6 : Inks according to Referential Examples 1 to 6 were prepared using their corresponding components as shown in Table 2 in the same manner as in Examples 1 to 6. Using each of the inks obtained in Examples 1 to 6 and Referential Examples 1 to 6, printing test was then conducted using, as an ink-jet recording apparatus, an On-Demand type ink-jet printer making use of a heating element as an ejection-energy source to evaluate the ink in (1) color tone, (2) clogging tendency, (3) density of a print, (4) bronzing tendency on a recording material, (5) water fastness, (6) resistance to feathering and (7) fixing ability in accordance with the following respective standards. The results are given in Tables 3 and 4. <Methods and Standards for Evaluation> (1) Evaluation of color tone: Solid printing was conducted on SK paper (Canon NP Dry SK) by the printer to observe the color tone of the resulting print by naked eyes. (2) Evaluation of clogging tendency (recovery property from crusting): The printer was left over for 1 month in a constant temperature chamber at 35°C, and then for 24 hours at room temperature. After conducting recovery operation (sucking operation by pumping), printing was conducted. The clogging tendency was ranked in accordance with the following standard: A: Normal printing state was recovered by conducting recovery operation at most 5 times; B: Normal printing state was recovered by conducting recovery operation 6 to 10 times; C: No ejection was observed even after conducting recovery operation 6 to 10 times, or print irregularity was noted. (3) Evaluation of density of print: Solid printing was conducted on SK paper (Canon NP Dry SK) by the printer and the resulting print was air-dried for 24 hours. Thereafter, the density of the print was measured by a Macbeth RD915 (trade name; manufactured by Macbeth Company) and ranked in accordance with the following standard: A: Print density was not lower than 1.30; B: Print density was 1.20 to 1.29; C: Print density was not higher than 1.19. (4) Evaluation of bronzing tendency on recording material: Solid printing was conducted on SK paper (Canon NP Dry SK) by the printer. After the resulting print was left over for at least 1 hour, the gloss of the solid printed area was observed by naked eyes to rank the bronzing tendency in accordance with the following standard: A: The print was lusterless and even in color strength; B: The print was partly lustrous and uneven in color strength; C: The print was entirely lustrous and uneven in color strength. (5) Evaluation of water fastness: Solid printing was conducted on SK paper (Canon NP Dry SK) by the printer. After the resulting print was left over for at least 1 hour, it was vertically immersed for 3 seconds in still water and then vertically pulled up to air-dry it in the interior of a room. Thereafter, the degree of redyeing due to running of dye to a blank was observed to rank the water fastness in accordance with the following standard: A: Neither redyeing nor smearing occurred on a blank; B: Redyeing occurred, and smearing was somewhat recognized on a blank; C: Redyeing occurred to a significant extent, and smearing was marked on a blank. (6) Evaluation of resistance to feathering: English characters and numerals were printed on SK paper by the printer, and the resulting print was left over for at least 1 hour. The print was then observed by a microscope and naked eyes to evaluate each ink in the resistance to feathering by ranking the degrees of sharpness of the letters and whisker-like feathering occurred on the letters in accordance with the following standard: A: The letters were sharp, and no whisker-like feathering occurred; B: The letters were dull, and whisker-like feathering slightly occurred; C: The letters were dull, and whisker-like feathering occurred to a great extent. (7) Drying time: English characters and numerals were printed on SK paper by the printer. After 15 seconds, 20 seconds, 25 seconds and 30 seconds, the printed area was rubbed with paper for lens-cleaning to measure the number of seconds required until the printed surface was no longer smeared, thereby ranking the fixing ability in accordance with the following standard: A: Not longer than 15 seconds; B: 16 to 25 seconds; C: Not shorter than 26. Example 1 2 3 4 5 6 Compound represented by Structural formula (a) (Y = SO 3 R) 2.7 2.5 2.6 Compound represented by Structural formula (a) (Y = H) 2.7 2.5 2 C.I. Direct Yellow 86 0.3 0.3 0.15 0.3 C.I. Direct Yellow 142 0.2 0.2 Ethylene glycol 10 6 Diethylene glycol 10 10 Thiodiglycol 5 5 Glycerol 8 6 10 7 Urea 7 5 7 5 5 6 Ammonium sulfate 0.6 0.6 0.5 0.7 0.1 1.0 Sodium hydroxide 0.6 0.4 0.5 0.4 0.15 1.0 Ethanol 5 5 5 5 Isopropanol 4 4 Water 73.8 64.3 73.0 76.2 77.6 72.1 Referential Example 1 2 3 4 5 6 Compound represented by Structural formula (a) (Y = H) 3 2.7 Compound represented by Structural formula (a) (Y = SO 3 H) 2 2.7 2.5 2 C.I. Direct Yellow 86 0.15 C.I. Direct Yellow 142 0.2 Ethylene glycol 10 Diethylene glycol 15 10 10 Thiodiglycol 5 Glycerol 10 8 2-Pyrrolidone 5 Ethylene glycol monomethyl ether 5 Urea 5 7 5 5 Ammonium sulfate 0.1 0.6 0.5 Sodium hydroxide 0.15 0.6 0.4 0.3 Ethanol 5 5 5 5 Isopropanol 4 Water 77.75 74.4 64.3 82.3 82.3 77.05 Evaluation item Example 1 2 3 4 5 6 Color tone Black Black Black Black Black Black Clogging tendency A A A A A A Density of print A A A A A A Bronzing tendency A A A A A A Water fastness A A A A A A Resistance to feathering A A A A A A Fixing ability A A A A A A Evaluation item Referential Example 1 2 3 4 5 6 Color tone RP RP RP RP Black Black Clogging tendency B A A C C B Density of print A A A A C A Bronzing tendency A A A C C A Water fastness A C A A A A Resistance to feathering A A B A A B Fixing ability A A B B A A Note: RP = Royal purplish. As described above, the inks according to the present invention are excellent in water fastness when conducting printing on all recording materials, in particular, so-called plain paper such as paper for copying, commonly used in offices and homes, and have an ideal black color. In addition, the inks can provide high-quality prints high in density and free of feathering, are excellent in solution stability, causes no clogging, and are good in storage stability and suitable for use as ink-jet inks.

Claims: An ink comprising a coloring material and a liquid medium dissolving the coloring material therein, wherein the coloring material comprises at least one of dyes represented by the structural formula wherein R is NH 4 and Y is H or SO 3 R, and at least one yellow dye selected from the group consisting of C.I. Acid Yellow 17:1,C.I. Acid Yellow 23, C.I. Acid Yellow 49, C.I. Acid Yellow 65, C.I. Acid Yellow 104, C.I. Acid Yellow 183, C.I. Acid Yellow 155, C.I. Acid Yellow 194, C.I. Direct Yellow 86, C.I. Direct Yellow 106, C.I. Direct Yellow 142 and C.I. Direct Yellow 194, and the liquid medium comprises at least one polyhydric alcohol and an aliphatic monohydric alcohol and contains urea, an ammonium salt of an inorganic acid and a hydroxide. The ink according to claim 1, wherein a mixing ratio of the dye represented by the structural formula (a) to the yellow dye is within a range of from 40:1 to 4:1 by weight. The ink according to claim 1, wherein the polyhydric alcohol comprises at least one selected from the group consisting of ethylene glycol, diethylene glycol, thiodiglycol and glycerol. The ink according to claim 1, which is suitable for use in ink-jet recording.

Inventors: EIDA TSUYOSHI, HATTORI YOSHIFUMI, KATSURAGI RYUJI, MAFUNE KUMIKO, MURAI KEIICHI, NAGASHIMA AKIRA, NISHIWAKI OSAMU, SAITO ERIKO, SANADA MIKIO, SATO SHINICHI, TAKIZAWA YOSHIHISA, TERAOKA HISASHI, TONOGAKI MASAHIKO, YAMAMOTO MAYUMI, YAMAMOTO TAKAO, EIDA, TSUYOSHI, HATTORI, YOSHIFUMI, KATSURAGI, RYUJI, MAFUNE, KUMIKO, MURAI, KEIICHI, NAGASHIMA, AKIRA, NISHIWAKI, OSAMU, SAITO, ERIKO, SANADA, MIKIO, SATO, SHINICHI, TAKIZAWA, YOSHIHISA, TERAOKA, HISASHI, TONOGAKI, MASAHIKO, YAMAMOTO, MAYUMI, YAMAMOTO, TAKAO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1994
Main classification: C09D11
IPC codes: C09D11